A Pembroke company is seeking an operating licence renewal with a plan to increase the amount of radioactive tritium it dilutes through the city's sewer system and the Ottawa River.

But tritium should not be discharged into the water at all, says a group of environmental organizations opposed to the relicensing.

The company, SRB Technologies, has a plant about 130 kilometres northwest of Ottawa where it makes glow-in-the-dark signs using tritium, a radioactive form of hydrogen.

Its final licence renewal hearing before the Canadian Nuclear Safety Commission will take place on Nov. 27, and commission staff have endorsed the renewal. However, the renewal will still have to be approved by the commission's licensing board.

The Canadian Coalition for Nuclear Responsibility and several like-minded groups held a news conference on Parliament Hill Tuesday to push for the plant to be shut down.

"Tritium is a known carcinogen," said Gordon Edwards, president of the coalition.

"We should not be dumping known cancer-causing substances into our drinking water."

The Ottawa River is the source of drinking water for communities along its banks, including Ottawa.

River water already contains tritium: company

But Stephane Levesque, president of SRB Technologies Canada, says the additional tritium the company plans to release will make little difference to existing levels, which are about five becquerels per litre, mainly from other nuclear facilities and tests years ago.

"With us releasing the additional amount of radioactivity, it will increase the concentration by 0.1 per cent at most," he said. "That would be 5.005 [Bq/L] and the drinking water guideline is 7,000."

Levesque said the company already discharges some tritium-contaminated water into the river, and the additional amount it is proposing is within its existing allowance.

The company is proposing an increase in order to prevent contamination such as that which caused the commission to temporarily shut down the plant in August.

That was when inspectors found radioactivity levels up to 80 times higher than what is considered safe in the groundwater near the plant. It's believed the source of the contamination was runoff from the plant and smoke stacks.

The company now says it will prevent future contamination by storing tritium-contaminated runoff and discharging it periodically through the Pembroke sewer system, where it will be diluted to acceptable levels before reaching the Ottawa River.

The environmental groups say they will be attending the Nov. 27 licence renewal hearing to make their case.